Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge.
Pedigree dog breeds are isolated and inbred populations each of which contain genetic diseases specific to the breed. While these diseases can often be a problem for breeders, they also serve as a valuable resource as models for genetic diseases in humans and other animals. In Australian Border Collies an autosomal recessive mutation resulting in a fatal neurodegenerative disease is wide spread in the population due to the common use of some champion carrier dogs. The condition is a lysosomal storage disorder known as neuronal ceroid lipofuscinosis (NCL), in which subunit c of mitochondrial ATP synthase accumulates (Jolly et al. 1994, J Small Anim Pract 35:299-306).
The neuronal ceroid lipofuscinoses are collectively recognized as the most common neurodegenerative disorder in children. Mutations have been identified in six different genes (CLNs 1,2,3,5,6,8) that each result in a unique form of the disease that is distinguishable by the age of onset and clinical course (Mole 1999, Lancet 354:443-445). The condition results in the lysosomal accumulation of an autofluorescent lipopigment that is mainly composed of subunit c of mitochondrial ATP synthase (Mole 1999, supra), except for the CLN1 mutation that results in the lipopigment containing high levels of saponins A and D (Tyynela et al. 1993, FEBS Letters 330:8-12). The ultrastructural patterns of these aggregates are variable and dependent on the gene mutated.
The CLN5 protein encodes a soluble lysosomal glycoprotein (Isosomppi et al. 2002, Hum Mol Genet 11:885-891) and it is suggested that it interacts directly with the proteins of CLN2 and CLN3 (Vesa et al. 2002, Mol Biol Cell 13:2410-2420). The protein displays no significant homology to any of the other NCL genes (Savukoski et al. 1998, Nature Genet 19:286-288) and is highly conserved between humans and mice, with the exception of the first exon (Isosomppi et al. 2002, supra; Holmberg et al. 2004, Neurobiology of Disease 16:29-40). Four disease causing mutations within the gene have been recorded in humans to date (Savukoski et al. 1998, supra; Holmberg et al. 2000, Neurology 55:579-581).
NCL has been identified in a range of animals including cow (Harper et al. 1988, Acta Neuropathol 75:632-636), dog (Koppang 1973, Mechanisms of Ageing and Development 2:421-445), horse (Url et al. 2001, Acta Neuropathol 101:410-414), and sheep (Jolly 1977, Med J 86:304-304; Tyynela et al.), although only in a few cases have the genetic mutations been identified. Naturally occurring NCL mouse models exist for CLN6 (Bronson et al. 1998, Am J Med Genet 77:289-297) and CLN8 (Bronson et al. 1993, Ann Neurol 33:381-385; Ranta et al. 1999, Am J Hum Genet 65:A5-A5), while knockout and targeted disruption models exist for the other identified NCL genes (Mitchison et al. 1999, Neurobiology of Disease 6:321-334; Gupta et al. 2001, Proc Natl Acad Sci USA 98:13566-13571; Sleat et al. 2003; Kopra et al. 2004, Hum Mol Genet 13:2893-2906). A mutation in CLN6 has been identified as the cause of a late-onset form of NCL in sheep (Broom et al. 1999, Molecular Genetics and Metabolism 66:373-375). The first large animal model of CLN5 has been identified recently in Devon cattle in Australia (Houweling et al. 2004).
Animals with NCL have revealed four additional genes as candidates for Border Collie NCL, although no mutations in the human homologues have been identified. Cathepsin D was first detected as a congenital form of the disease in sheep (Tyynela et al. 2000, Embo J 19:2786-2792), and further studied using knockout mouse models (Koike et al. 2000, J Neurosci 20:6898-6906). Additional mouse models have shown that mutations within PPT2 and CLC-3 also produce NCL (Gupta et al. 2001, supra; Yoshikawa et al. 2002, Genes Cells 7:597-605). Additionally, radiation hybrid mapping (Breen et al. 2001, Genome Res 11:1784-1795) of the microsatellite markers linked to the English setter NCL gene (Lingaas et al. 1998, Anim Genet 29:371-376) indicated the gene is located to a region that does not contain any homologues of any of the identified NCL genes.
Although onset of NCL in Border Collies may be observable to owners as early as 16 months (Studdert and Mitten 1991, Aust Vet J 68:137-140), the age of onset and severity can vary greatly between siblings. As the extent of neurodegeneration increases, all affected dogs develop psychological abnormalities and ataxia. The clinical course includes increasing levels of nervousness and possible outbursts of aggression, hallucinations (displayed as fly biting), hyperactivity and epileptic fits. Most animals lose their ability to coordinate everyday muscular activities, such as house training, walking and eating (Studdert and Mitten 1991, supra; Jolly et al. 1994, supra). Complete blindness only occurs in some cases, with changes in the eye only observable through ultrastructural examination of the retina where fingerprint and curvilinear patterns predominated within lysosomal aggregates (Taylor and Farrow 1988, Acta Neuropathol 75:627-631). Due to the debilitating nature of the disease, Border Collies suffering from NCL rarely survive beyond 28 months (Studdert and Mitten 1991, supra).
Accordingly, there is an ongoing need to identify the mutations which cause NCL in mammals, and in particular border collies. In work leading up to the present invention, a variant form of CLN5 has been identified, the expression of this variant being associated with the onset of NCL in dogs, in particular in border collies. These findings now provide highly specific genetic and protein based diagnostic means. Since it has been determined that NCL is associated with the expression of this variant form of CLN5, there is also enabled the development and/or use of animal models expressing this CLN5 variant for the development or analysis of, inter alia, therapeutic or prophylactic treatments. Still further, there is also provided means for the in vitro screening for modulatory agents which may be useful for therapeutic or prophylactic application, such as agents which block the expression or functioning of the mutated form of CLN5 thereby enable normalisation of CLN5 levels via administration of the non-mutated protein expression product.